This section features a discussion of four computers whose impact on
computer structures is still being felt today: the Manchester Mark 1, the
PDP-8, the B 5000, and the Atlas. It also provides detailed examples of
the concepts already introduced, including ISP, PMS, and Kiviat graph notations
and the concepts of digital system hierarchy and computer classes.

The four computers are arranged in order of size. The Mark 1, if constructed
with contemporary technology, would be a monolithic microcomputer. The
PDP-8, fabricated on a single CMOS chip (Intersil 6100), is a contemporary
microcomputer. The B 5000 would be considered a contemporary minicomputer.
(The discussion of the B 5000, supported by PMS diagrams and Kiviat graphs,
traces the evaluation of a computer family. Computer families will be discussed
more extensively in Part 4.) Finally, the Atlas pioneered many of the concepts
implemented in maxicomputers.

This section encapsulates Parts 3 and 4 of the book. As is the convention
throughout Parts 3 and 4, it begins with critiques of each computer.

The Manchester Mark I

The Mark 1 was the world's first stored-program computer. It
executed its first program on June 21, 1948, ushering in a new technological
revolution of major impact for the next three decades. Chapter 7 describes
the organization and ISP of the Mark 1, the simplest ISP in this book.

The PDP-8

The 12-bit PDP-8 was the first mass-produced minicomputer, setting the
standard for its class. The PDP-8 is considered in depth because:

1 It has a simple but nontrivial ISP, whose influence still affects
such contemporary architectures as the Hewlett-Packard HP 2100 series and
the Data General NOVA series. Study of this ISP will help the reader understand
the general ISP concept. The same is true for its simple but nontrivial
PMS structure.

2 The implementation is simple enough to illustrate clearly the complete
set of levels in the digital design hierarchy: PMS, programming, logic,
and circuit. Only a few other single examples in this book will be able
to illustrate several levels in the hierarchy (e.g., the HP 9845, Chap.
31; the TMS1000, Chap. 34; the PIC1650, Chap. 35; the PDP-11, Chap. 38;
and the HP 9810/20/30, Chap. 49).

A discussion of the entire PDP-8 family can be found in Chap. 46. Figure
1 is the Kiviat graph for the PDP-8.

The B 5000, a Stack Machine

The B 5000 is an outstanding example of stack organization and memory
segmentation. (The following comments concern the P. stack computers manufactured
by both English Electric and Burroughs; a discussion of memory segmentation
is postponed until Part 2.) There are four basic P.stack computer families:
B 5000 ® B 5500 ®
B 6500/B 7500; D825 ® D830 ®
B 8500; KDF 9; and B 6700/B 7700. Root members of the first three families
were made available at about the same time by Burroughs of Pasadena, California,
Burroughs of Paoli, Pennsylvania, and English Electric. The IBM Corporation
later responded with a proposed Pc.stack, but the machine never entered
the production phase. The Hewlett-Packard HP 3000 is a stack-based minicomputer.